Rotodynamic turbo machines are provided in several known constructions such as Voith-Schneider ship propellers, Darrieus and Savonius rotors for wind turbines, the Ossberger or Mitchell turbines for water drive and the so called transverse current or cross flow fan. The Voith-Schneider propellers usually have rotor vanes which can be re-adjusted when rotating.
In a rotor which is traversed by a flow transversally to its rotational axis and which is relatively sparsely fitted with vanes, there must in general exist the possibility to turn ("to angle") the vanes relative to a tangent to their circular path. The character and the degree of the angular adjustment is in every position of the vanes governed by the condition that a line which is normal to the plane in which a vane extends (i.e. to the plane of symmetry of a vane which generally has profiled shape) shall at least approximately pass through a so called control point. In the Darrieus rotor e.g. the control point is located on the rotational axis of the rotor and the vanes have a fixed position, so that these planes always lie tangentially to the circular path of the vanes.
Adjustment of the vanes of a turbine is desirable partly to obtain a sufficiently great starting torque, partly in order to be able to regulate the output effect and/or the number of revolutions as required, and partly in order to be able to avoid overloading when the medium flowing through the rotor has a too great inflow velocity. When transverse flow machines are not used as turbines, but as pumps, fans, agitators and the like, the possibility to re-adjust the vanes enables the capacity to be readily changed as required and with an only insignificant deterioration of efficiency.